This is Ronnie Montrose and his band known as Montrose, circa 1974, that included Sammy Hagar at the time.
I agree 100% with one of the many comments on YouTube that said this about this song: "This the genuine article. No effects, synth, overdubbing, just great musicians. They didn't even need a second guitar. Kids should watch this so that they know what musicianship really is." Enjoy! GC